Dam construction



F. A. NOETZLI DAM CONSTRUCTION.

APPLICATION FILED JUNE 16, 1919.

' Patented Mar. 21, 1922.

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APPLICATION FILED JUNE I6, 1919- I I I 1 410 211 Patented Mar. 21, 1922.

2 SHEETS-SHEET 2.

MTf/E'J 5: A INVENT R' av /swam must) STATES has.

aris FRED.A NOETZLI, OE OAKLAN'D, CALIFORNIA.

DAM CONSTRUCTION.

Specification of Letters Patent.

Patented Mar. 21,1922.

Application med Julie 1c, 1919. Serial ste m.

To all whom it may concern:

FRED A. Non'rzm, a

Be it known that I,

residin at Oakland,

citizen of Switzerland,

fornia, improvements which the following is a specification.

lilhis invention relates to improvements in dams and more particularlyto masonry dams of the archltypel and it has for its object to builddams safer and more economi-cally. An arch clam may be considered eitheras an arch reaching from top to bottom, or as a plurality 'of superposedarches.

In the single or multiple arch dams which heretofore have beenconstructed, it has been shown that there is the tendency in the lowerparts of the dam to produce open cracks either between foundation andmasonry or higher up in the masonry itself and in more or lesshorizontal directions. Many among these curved dams also have developedvertical cracks in the upper portions due to shrinkage and temperaturestresses. In no dam built thus far, to the best of my knowledge, existsan economical and harmonious cooperation between vertical cantilever andhorizontal arches, the. Vertical cantilever in arching dams always beingbuilt'too stiff,

though not strong enough, to support its share of load. The result wasthatthe cantilever cracked and deflected until the horizontal archeswere able to get into action and relieve the cantilever, thus preventingultimate failure; The objects of my invention are, first, .to provide aneconomical divisionof waterpressure between vertical cantilever andsuperposed horizontal arches by giving the cross section of the dam aspecial shape and varying the radius of the horizontal arches in aspecial way; second, to anchor the dam by means of steel bars to therock'foundation or to a special foundation built of masonry third, tobuild single arch dams overhanging in a downstream.-

direction: and fourth, to construct arched dams with a core-of masonrystronger than concrete, and covered on one or both sides with areinforced concrete slab.

Other objects of my invention will be hereinafter set forth and moreparticularly pointed out in the appended claims.

in the accompanying drawings, in which my improved dam is illustrated,

Figure 1 is a down-stream elevation of the improved arch dam;

Fig. 2 is a section on line 2-2 of Fig. 1;

Fig. 3' is a section on line 3-3 of Fig. 1; Fig. t shows the deflectionlines of vertical and horizontal arch slices in a vertical plane.

Fig. 5 IS a cross section of a dam showing the method of anchorage;

Fig. 6 shows in detailv one method of anchorage;

Fig. 7 shows asecond method of age;

Fig. 8 shows a third method of anchorage; -Fig. 9 is ahorizo'nt-alsectionthrough a dam with special masonry was? Fig. 10 is a;horizontal section through a dam reinforced by concrete slabs castagainst up and down-stream faces of said dam.

Similar letters and numerals refer to similar parts throughout theseveral views.

Referring now to Fig. 1, a curved dam A. is shown which rests on anenlarged case B and abuts sideways against the hillsides either directlyupon the solid. rock or upon a continuation of the enlarged base B whichprovides a smooth and-uniform bearing for anchorthe arches withoutabrupt changes in the arch spans.

If the horizontal arch were subject radial water-pressure only, thethickness of an arch dam would have to be uniform in every horizontalplane Temperature and shrinkage forces produce additional stresses inevery horizontal archslice and it can be proved that these secondarystresses are much greater near the arch abutments than near the crown.The thickness of the horizontal arch slices therefore has to beincreased towards the abutments to obtain a structure of uniformstrength. To obtain this, I choose the center 1 for the circularupstream face at a point farther down "earn than the center 2 for thecircular townstream face, all as shown in Fig. .2.

Referring-now to Fig. 3, wherein is shown a cross section of the darn.on the line 3--3,

the arch A is supported by the enlarged base 33 and well anchored tosaid base it by means of the reinforcing bars 3 which may extend for anylengtlrup into the arch and suil iciently down into the base :8to'insure a safe bond. The cross section of the arch is shown of aboutuniform thickness in the near 5 or even higher up would be toosmalllower part 4 just above the base B, to provide for a flexiblecantilever. Farther up near 5 the thickness of the arch is increasedsomewhat to provide for a very strong middle arching part.

Theory shows that an arch dain in the lower portion 4 acts mainly as'avertical cantilever. This portion 4 thereforehas to -be rather-slenderto produce enough deflection near 5 so that horizontal arch action maydevelop. Figure 3 showsthe cantilever part 4 subdivided into a pluralityof substantially parallel walls; purpose of making thecantilever moreflexible. Further, the thickness of the dam about midway between its toand base is increased somewhat thus provi ing suflicient strength forthe arches. In the really arching portion of a curved dam, i. e. from 5to the top of the dam, the lowest-portion 5 of these arches has to bethe strongest. Therefore there exists the necessity of having a slendercantilever in the lower portion 4 of a dam and suflicient strength in ahorizontal direction where arching starts to prevail. It is often ofadvantage to make portion 5 stronger than any other part of the dam'abox e the base.

If we would increase also the thickness of the cantilever part 3 of sucha dam, this would have the undesirable effect of making the cantileverso stifi' that itsdeflection ator to allow appreciable arch-action toevelop. Thus more load would-be thrown upon the cantilever than it mightbe able to carry, unless it be made of-full gravity section as thisalone enables a dam to sustain full water-pressure without 'materialhelp from horizontal arching.

The up ermost portion 6 of a slender arch dam pre erably is madeoverhanging in a down-stream direction. .rangement the weight of the damportion 6 will prevent the opening of shrinkage cracks. In most existingsingle arch dams vertical cracks occur due to excessive tensiletemperature and shrinkage stresses. This greatdisadvantage is overcomesuccessfully by making an arched dam sloping entirely or partially in adown-stream direction.

Referring now to Fig. 4, wherein are shown the deflection lines ofvertical cantileverand horizontal arches in a vertical sectionfof acurved dam, it ma be assumed for the'purpose of stati'cal esign that anarch dam consists of a series of vertical dam slices, acting ascantilevers. and a series ofhorizontal arch slices. I

Let us consider asan example a vertical 1 section at the centerof thedam. Under the assumption that the horizontal arch slices have to carryall the load, andconsidering also that under the influence of a drop intemperature and the shrinkage in the con- This is for the.

With such an ar-'.

crete the arches are shortened, the arch crowns may come into theposition given by the line a in Fig. 4. On the other hand, if thevertical cantilever without breaking were able' to .and really had tosustain without the help of the upper arches all the water-pressurewhich falls upon it on account of its stifl'ness near the bottom, wherepractically noarch action can develop, it would deflect elasticallyalongthe'line c. If the vertical cantilever "and the horizontal archeswork together, the resulting real deflection line is about in theposition of the line a. an deflections are plotted horizontally from avertical axis 3)..

In designing an arched masonry dam, we have to assume that part of thewater-pressure is supported by vertical cantilever action and part byhorizontal arching. It can be, shown that in an economically designedarch dam cantilever action prevails inthe lower part 4 and arching inthe upper part 6 of thedam. In 'no single arch dam, built there existsan ieconomicaldivision of the water-pressure between vertical cantileverand horizontal arches, the latter carrying .very little. or no load atthe time of low temperature, unless the vertical cantilever be cracked.'By varying in an arch dam the thickness of the dam. and the radii ofcurvature of the axis of the horizontal arch slices in such a way thatthe elastic cantilever deflection line 0 intersects the arch crowndeflection line a, more economical conditions are obtained for thedimensions of such a dam. At the same time the vertical canti- L leverhas to be anchored sufiiciently to the foundation that no cracks areproduced at or near the base of the dam.

It can be proved, that all of the existing arched dams either do notdevelop any horizontal arch action at the time of low dam temperature,.or that they can do so only after the cantilever has cracked partially,in general in opening cracks between foundation and masonr Not to myknowledge has ever enough, i any, steel reinforcement been placed inthese parts of excessive tension in a dam as, no method was known tocompute those stresses. a V

5, 6, 7 and 8 illustrate alternative schemes how the base of a dam Dmaybe the vertical cantilever is able to carry its share of waterpressure without breaking away from the base. Fig. 5; shows the -methodof anchoring a dam of-"any shape. Fig. 6, shows a detail of Fig. 5. Ahole 7 is drilled into the r'ock R- and a metalhar 8 introduced intosaid hole which is afterwards filled with cement -mortar. Fig. 7 showsthe steel bar 8, set into the hole 7 and protected by a tube 9 ofnoncorrosive material, such as galvanized iron pipe, tar paper anchoredto the rock foundation R so that .trench lO is excavated near thetip-stream or down-stream face of the dam, this trench being filled withmasonry, into which metal bars 8 are anchored by bending them aroundother metal bars 8 which lie in the longitudinal direction of thetrench.

Referring now to Fig. 9, wherein is shown a partial horizontal sectionof an arch dam, the fact that the temperature stresses in an archedstructure increase with the third power of the thickness of the arch,makes it very desirable to buildarched dams as thin as possible. it istherefore often of advantage to use a better quality of arch materialthan common concrete,to give a structure suficient strength in directaxialcompression'. Well coursed masonry of granite, etc., is verysuitable for this purpose and the material in general is readilyavailable near every dam site. Nevertheless, in first class masonryarches, tension is liable to occur at certain places, due to temperaturedeformations. Masonr other than concrete cannot very well be reinforcedby steel bars to take care of tensile stresses. l prefer to carry outthis feature of my invention b casting concrete slabs 11 against the laimasonry 12, and embedding safely into said concrete slab any number ofsteel bars 13 and in any 'direction that maybe found desirable. Toprovide a good bond between said concrete slab 11 and the masonry core12, I introduce additional steel bars 14 in more or less radialdirection passing throu h or part through the masonry core 12 ah wellanchored into the concrete slabs 11, or fastened to the bars 13. Beforecasting the concrete slabs 11 against the masonry core 12, I cover theexterior of said masonry core 12 with a thin watertight layer 15 ofmortar, applied with a cement gun.

Referring now to Fig. 10, wherein is shown a partial horizontal sectionof an arch dam, many arch dams through incor rect design or constructionhave .developed cracks, which under the influence of temperature changesand the varying waterpressure open and close periodically. Thisendangers the stability of the structure. I improve the strength of sucha dam by casting concrete slabs 11 against the faces 16 of the existingdam 17 and embed in said slabs 11 sufiicient metal reinforcement '13 totake care of the tensile stresses occurring in the arch under pressure.To insure a good bond between the existing masonry core 17 and the newconcrete slabs 11, I drill holes 18 into said existing core 17 andanchor steel bars 19 into the holes 18', said bars extending well intothe slabs 11, being fastened eventually to the slab'reinforcement 13.

I am aware that prior to my invention dams have been built which possesscertain. features in part similar to the ones described above. Itherefore do not claim such combinations broadly; but

1 'claim 1. A single-archdam having preponderantly cantilevering I andpreponderantly arching parts, the thickness of said dam in horizontalplanes being greater near the abhtments than near the crown.

2. An archdam of such a shape that horizontal planes out both upstreamand downstream faces of said dam along lines whichareisubstantiallycircular in form, the centers of these circles beingnon-coincident,

the center of the down-stream circle lying further rip-stream than thecenter of the up-stream circle.

3. An arch dam of varying radii of curvature, said dam being thicker atupper elevations than at lower-ones, substantially as described.

4. An arch dam comprising a plurality of superposed arches, thethickness of such arches being larger in upper horizontal planes than inlower ones, such, arches in the upper portion of said dam projecting outin varying amounts beyond other arches below.

5. A reinforced arch dam comprising superposed arches, the thickness,reinforcement and strength against axial compression of such archesbeing larger in upper horizontal planes than in lower ones substantiallyas described. 7

6. An arch dam comprising a preponderantly cantileveriiig and apreponderantly arching part, said cantilevering part being subdividedinto a plurality of walls substantially parallel to the axis of the dam.

7. A reinforced concrete arch dam comprisingsuperposed arches and aplurality of vertical cantilever slices, the thickness of such archesbeing larger in upper horizontal planes than in lower ones, saidcantilever slices deflecting elastically under their share of the waterload at any elevation of the dam substantially as much as said arches atthat same elevation, if said arches have to support the full water loadand also are shortened by a decrease of temperature at the dam crest ofnot less than 15 Fahr. be-

low the closin temperature of the darn, substantially as escribed.

8. An arch dam comprising a pre onder antly cantilevering and a preponerantly arching part, said arching part comprising superposed arches,the thickness of such arches being larger in upper horizontal planesthan in lower ones, the cantilevering part of said dam being anchored tothe rock foundation by means of metal bars.

9. In an arch dam the combination of an enlargedbase of masonry and aplurality of superposed arches, the thickness of such arches beinglarger in upper horizontal planes than 1n lower ones, said arches beinganchored to said enlarged base by means of metal bars.

10. An arch dam comprising a plurality of superposed arches, thethickness of such arches being larger in .upper horizontal planes thanin lower ones, said arches having a core of rubble masonry, concreteslabs placed against said core, said concrete slabs being reinforced bymetal bars.

11. An arch dam havin both faces inclined in a down-stream direction,the said dam being thickest in vertical planes at a point intermediateits top and base and having its base portion subdivided into' aplurality of vertical parallel planes.

12. An arch dam having both faces inclined in a down-stream direction,the thickness of said dam in any "horizontal plane being greatestadjacent the abutments and the thickness of said dam in tvertical planesbeing greatest at .a point intermediate its 4 Witnesses.

FRED A. N OETZLI. \Vitnesses H. E. LINDEN, IvAR BULL LMoN-TE.

